This invention is directed to a microwave oven comprising means for browning a piece of food, an oven cavity, a microwave source and a feeding system for supplying polarized microwaves to the cavity. The invention is also directed to a rotating browning plate for use in a microwave oven having a rotating bottom plate in the load zone of the oven cavity and, adjoining the cavity bottom, an input opening in a sidewall of the cavity for supplying polarized microwaves with an E-field which is substantially vertical.
1. Field of the Invention
A general problem when preparing food in microwave ovens is the difficulty in obtaining browning or a browned surface on the food. Many proposals to the solution thereof have been developed among others in the shape of accessories to the microwave oven, specifically shaped vessels for use in the oven, as well as specifically shaped packings for prefabricated dishes on the one hand. A specific problem of these accessories, vessels and packings is the influence thereof on the propagation of microwaves in the cavity and a consequent risk of an inferior cooking result in comparison with the situation when the cooking takes place without such facilities. Changes of the microwave propagation may also bring with it a decreased microwave efficiency in the oven. In consequence thereof problems will arise in obtaining a rapid and even heating, which may bring with it among other things an overheating of edge areas.
2. Description of the Related Art
From the U.S. Pat. No. 2,138,162 it is previously known to convert microwave energy to heat energy by using a ferrite material which may be arranged on the underside of a vessel. Measurements in order to speed up and improve the efficiency of the energy absorption are not disclosed in the publication. The SE patent specification no 343742 is also based on the use a ferrite material in a so called absorbator, which may comprises a free plate alternatively being arranged at the bottom of the vessel. In the microwave oven disclosed therein the absorbator is supplied with microwave energy via a so called microwave applicator, being specifically adapted for the purpose. The disclosed construction of the applicator, as well as the microwave oven comprising the same, however, have a technical structure which is complicated and cost demanding. EP-A1-0317203 describes a plate of a microwave energy absorbing material, in which regions are obtained having different "loss characteristics", partly absorbing microwave energy, partly providing a coupling to the microwaves and initiating thereby higher modes of oscillation propagation in the food piece/load which is placed on the plate. Measurements in order to speed up and improve the efficiency of the heating progress have not been disclosed. One further example of the prior art is found in U.S. Pat. No. 4,369,346 which discloses a ceramic plate specifically shaped for baking purposes, for example baking of pizzas. In the ceramic material on the under side of the plate a pattern of microwave absorbing areas have been provided by means of ion implantation into the ceramic material.
Examples of the specifically designed packings for use in microwave ovens are disclosed in U.S. Pat. Nos. 3,302,632, 4,594,492, and 4,676,857. In these packings parts of the packings have been fitted by the use of metal foil etc in order to obtain the desirable heating, browning and crisping effects. Such packings, however, only to a small extent are related to the invention.
All of the prior art solutions, except SE 343742, are lack of adaption between the proposed facilities and the propagation of microwaves in the oven in which the same are intended for use.